Re: Relationship between magnitude and distance

As far as I know, the answer is no. There are all sorts of factors that go into
a galaxy's brightness - types of stars present, dust present, orientation, et
al. That affects the galaxy's brightness more than distance does, although
distance does affect it also.

And it's the opposite with edge-ons. You're getting LESS starlight because one
star blocks the light from another. You can't see stars behind other stars.
And don't trout out the argument that they're just made of plasma and gas.
Aside from the fact that plasma can absorb light just as well as solid matter
under the right conditions, try looking through a cloud sometime.

--- Dave
--
----------------------------------------------------------------------
Pinprick holes in a colorless sky
Let inspired figures of light pass by
The Mighty Light of ten thousand suns
Challenges infinity, and is soon gone

david.nakamoto@xxxxxxxxxxx


"Martin R. Howell" <martinhowell@xxxxxxxxxxxxxxxxx> wrote in message
news:vuerihvjjd0b.1f6uq51fetqn.dlg@xxxxxxxxxxxxx
>
>
> Last night I was enjoying the view of two galaxies, NGC5740 and NGC5746.
> Both fit into the same field of view in a wide angle EP. NGC5746 is a
> splendid edge-on while NGC5740 assumes a more typical orientation. I was
> struck by the differences in brightness. Located in an approximately 4.1
> NELM of my night sky, NGC5746 was fairly easy to pick out with a 9mm
> eyepiece while NGC5740 was very tough to discern. Now, it would seem to me
> that even if both had the same absolute magnitude if it were possible to
> "flip" 5746 into the same orientation as 5740, wouldn't 5746 be brighter to
> my eye simply because it is observed edge-on? More importantly, knowing
> that galaxies come in all sizes, different shapes, and distances from us,
> is there a general rule of thumb which roughly matches visual magnitude
> with distance? For example, would a person be horribly way off in assuming
> that the "average" 12th magniutde galaxy is maybe 85 to 100 million light
> years away while the "average" 13th magnitude galaxy is around 100 to 125
> million light years distant? The distances I just cited are ones which
> were made up for illustration of my point and question. Again, I am
> talking about some average galaxy size and taking into account a common
> orientation to our line of site for that galaxy.
>
>
> --
> Martin R. Howell
> "Photographs From the Universe of Amateur Astronomy"
> http://members.isp.com/universeofamateurastronomy%40isp.com


.

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